Just like last year, the Bears might be forced to keep a key player on the physically unable to perform list when the season starts. Last year, it was rookie Kevin White, who ended up missing the entire season due to a shin injury. This year, it might be their best defensive player.

According to NFL Network's Ian Rapoport, outside linebacker Pernell McPhee could miss the first six games of the season as he works his way back from offseason knee surgery.

For a Bears team lacking depth at nearly every position -- like most teams in the second year of a rebuild -- this is the kind of injury that can derail a season, especially if it lingers past six games. In 14 games last year, McPhee notched six sacks. Pro Football Focus graded him as the third-best 3-4 outside linebacker against the run and the most productive pass-rusher. That's who the Bears might be without after finishing last season with the second-worst defensive DVOA, according to Football Outsiders.

In his absence, Lamarr Houston's role will likely increase. Houston recovered from an ACL tear during a portion of last season, but rebounded nicely with eight sacks. So, Houston's not the worst replacement -- plus, McPhee's absence might mean more snaps for rookie pass-rusher Leonard Floyd -- but that doesn't change the fact that the Bears are quickly losing bodies on the defensive side of the ball.

The secondary is a mess. Kyle Fuller underwent knee surgery this month and is out indefinitely. Tracy Porter suffered a concussion in the Bears' most-recent preseason game. Nickel cornerback Bryce Callahan is also battling injuries. Those are the Bears' top three corners. Even if all three were healthy, the secondary still would've been the weakness of a revamped defense. And, oh yeah, they open up the season against DeAndre Hopkins and the Texans.

The reason the Bears' secondary woes relate to McPhee? The best way to negate a struggling secondary is to apply consistent pressure, and McPhee would've helped defensive coordinator Vic Fangio do just that.

That's not to say the Bears' season is already lost -- this isn't as significant as Vikings quarterback Teddy Bridgewater's knee injury, of course. General manager Ryan Pace already worked a miracle in retooling the front seven in two offseasons and the Bears hung with playoff teams a year ago, even before Pace added players like Danny Trevathan, Jerrell Freeman, and Akiem Hicks. It is, however, a setback for a team that can't afford to experience injury issues if it wants to compete for a playoff spot this winter.